Fishing capacity measures the capability to catch fish. Capacity utilization is the actual effectiveness in catching fish; the ratio of catch to capacity. The factors comprising a fleet's capacity are the number and size of vessels, the technical efficiency of those vessels, and the time commitment of fishermen. Knowing the capacity utilization of a fleet is critical for evaluating management alternatives. This is true regardless of whether fisheries are managed with fleet controls or with individual controls. We illustrate the measurement of capacity utilization with the Oregon bottom trawl fishery, in which fleet capacity quadrupled between 1976 and 1982. From 1982 to 1985 capacity declined 30% due to economic problems in the industry and vessels finding better opportunities elsewhere. Capacity measurement is necessary to assess management-induced changes in controlled fisheries. Controlling capacity requires addressing all the elements associated with capacity growth. Examination of the components of fleet capacity reveals an array of management options.